docs(optimizr): add logo and fix rtd deps

docs/source/api/grid_search.md

@@ -0,0 +1,14 @@
+# API: grid_search
+
+```python
+from optimizr import grid_search
+
+best_params, best_score = grid_search(
+    objective_fn,
+    param_grid,
+)
+```
+
+- `objective_fn`: callable receiving a dict of parameters and returning a scalar loss
+- `param_grid`: dict of name -> list of values to enumerate
+- Returns `(best_params: dict, best_score: float)`